Figure 2.

Correlation between the signal quality indices based on the adjudicated photoplethysmogram (PPG) signals. (a) excellent PPG signal quality (G1) versus acceptable PPG signal quality (G2); (b) G1 versus (G2 and unfit to diagnose PPG signals (G3)); and (c) G1 versus G3. Signal quality indices: perfusion (${\mathrm{P}}_{\mathrm{SQI}}$), kurtosis (${\mathrm{K}}_{\mathrm{SQI}}$), skewness (${\mathrm{S}}_{\mathrm{SQI}}$), relative power (${\mathrm{R}}_{\mathrm{SQI}}$), non-stationarity (${\mathrm{N}}_{\mathrm{SQI}}$), zero crossing (${\mathrm{Z}}_{\mathrm{SQI}}$), entropy (${\mathrm{E}}_{\mathrm{SQI}}$), and the matching of systolic wave detectors (${\mathrm{M}}_{\mathrm{SQI}}$). Here, the red color and the blue color indicate strong correlation and anti-correlation, respectively.